I agree, although, I think the difference is a reddit-like site needs a far smaller critical mass of users to get by than twitter/mastodon. You just need enough to people to fill out some major communities, and enough that you can find a group of people for your niche.
It's why I'm sort of not worried if there is some mass exodus from reddit. We are getting enough to bring life to this area of the fediverse and that's great.